JP2711973B2 - Manufacturing method of zinc-based electroplated steel sheet with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a zinc-containing electroplated steel sheet containing Cr and having excellent corrosion resistance, which is used for automobiles and home appliances.

[0002]

2. Description of the Related Art Electrogalvanized steel sheets are used in automobiles, home appliances,
Widely used mainly for building materials. Of these, in automobile applications, higher corrosion resistance is required in order to prevent vehicle body corrosion due to scattered rock salt for preventing road freezing in winter in cold regions. Corrosion resistance of galvanized steel sheet can be improved by increasing the amount of zinc plating (adhesion).
This has many problems in terms of weldability and workability. Therefore, many alloy platings have been proposed as a method of suppressing the dissolution of zinc itself and extending the life of zinc plating. Above all, F
Zn-based alloy plating containing e, Ni, and Co as alloy components is recognized for its good bare corrosion resistance and corrosion resistance after painting, and has been put to practical use. Further, Japanese Patent Application Laid-Open No. 61-27039
No. 8, Japanese Patent Application Laid-Open No. 62-54099, Japanese Patent Application Laid-Open
As disclosed in JP-A-120393 and the like, Zn
Attempts have also been made to include Cr in the Zn-based alloy plating, but this has not been superior to Zn-Ni alloy plating or Zn-Fe alloy plating in corrosion resistance.

[0003]

Attempts to precipitate Cr together with zinc have conventionally been made using Cr ³⁺ or Cr ⁶⁺ ions, but only a small amount of Cr precipitates from a simple bath. Several% of C due to increase of Cr concentration and current density
Even when r is precipitated, not only good appearance is not obtained, but also there is no industrially advantageous method accompanied by remarkable reduction in workability and current efficiency. The present invention solves the above problems, and
An object of the present invention is to provide a method for producing a zinc-based electroplated steel sheet having excellent corrosion resistance containing r.

[0004]

The gist of the present invention is as follows. (1) In producing a galvanized steel sheet containing Cr, 0.1 to 10 g / volume of Zn ²⁺ ion, Cr ³⁺ ion and vanillin or a derivative thereof. l , pH
With a plating bath of 0.5 to 3.0, a current density of 20
Method for producing a superior zinc electroplated steel sheet in corrosion resistance, characterized in that at ~150A / dm ² perform electroplating. (2) In producing a galvanized steel sheet containing Cr, 0.1 to 10 g / l of Zn ²⁺ ion, Cr ³⁺ ion, vanillin or a derivative thereof, and 0.00 to 0.1 g of a cationic polymer and / or a polyoxyalkylene derivative.
Excellent corrosion resistance characterized in that electroplating is performed at a current density of 20 to 150 A / dm ² using a plating bath containing 1 to 20 g / l and having a pH of 0.5 to 3.0 . This is a method for producing a zinc-based electroplated steel sheet.

[0005]

The use of a simple bath of conventional Zn ²⁺ ions and Cr ³⁺ or Cr ⁶⁺ ions only precipitates a small amount of Cr.
Even when r was precipitated, the margin of improvement in corrosion resistance was small, and plating that could withstand practical use in terms of appearance and workability could not be obtained.
However, by adding vanillin or a derivative of vanillin as a Cr deposition accelerator to a zinc-based plating bath containing Cr ³⁺ ions, this problem was solved, and a large amount of Cr was added.
Thus, plating having a high corrosion resistance including the above can be obtained. The reason is presumed to be that vanillin forms a complex with Cr ³⁺ ions and facilitates the precipitation of Cr ³⁺ ions while suppressing the precipitation of Zn ²⁺ ions. The addition amount of vanillin or a derivative of vanillin is preferably 0.1 to 10 g / l, and if it is less than 0.1 g / l, the effect of Cr precipitation is not sufficient. is not. Here, vanillin is C ₈ H ₈ O
An organic compound represented by ₃ ,

[0006]

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The derivatives of vanillin include vanillic acid, vanillin oxime, and esters thereof.
Vanillin and its derivatives may be used alone or in combination. In the plating bath, a cationic polymer or a polyoxyalkylene derivative may be further added in addition to these vanillins, whereby the appearance quality can be improved, and it is more advantageous for Cr precipitation. . The addition amount of these is preferably 0.01 to 20 g / l, and if the addition amount is less than 0.01 g / l, the above effect is insufficient and 20 g / l
If it exceeds / l, the Cr precipitation effect is saturated. Either the cationic polymer or the polyoxyalkylene derivative may be used, or both may be used.

[0008] As the cationic polymer, the following quaternary
Polymers of amine salts are preferred, especially polyamine sulfones
(Abbreviated as PAS) and polyamine (abbreviated as PA) are effective
is there. The reason for this is that amine groups absorb
Adhesion and Cr on sulfone groups ³⁺Coordination bond of ion contributes
It is estimated that The average molecular weight is 10^Two ~ 1
0⁶ Is preferred.

[0009]

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[0010]

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[0011]

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The polyoxyalkylene derivative is represented by R ₂ —O
It is an organic compound represented by-(R ₁ -O) _n -H. The average molecular weight, 10 ² to 10 ⁶ are preferred. Among them, polyethylene glycol (abbreviated as PEG) HO-
(CH ₂ —CH ₂ —O) _n -H is effective.

FIG. 1 shows the relationship between the amount of the Cr deposition accelerator added and the Cr content in the plating layer, and FIG. 2 shows the relationship between the amount of the Cr deposition accelerator added and the appearance of the plating film obtained. . The conditions other than the amount of the Cr precipitation accelerator added, that is, the plating bath composition and the plating conditions are constant. Vanillin 0.1g
/ L, the Cr content is about 1%, but 0.1 g
/ L or more, the Cr content becomes 5% or more. Also,
When 1 g / l of PA is added as an example of the cationic polymer, the Cr content tends to increase as compared with the case of vanillin alone, and a glossy uniform appearance is obtained.

The type of plating bath is not particularly limited, but a sulfate bath, a chloride bath, and a mixed bath thereof are preferred. The metal ion concentration is preferably 30 to 200 g / l in total of Zn ²⁺ ions, Cr ³⁺ ions, and iron group metal divalent ions. If it is less than 30 g / l, the supply of ions tends to be insufficient at a high current density, and as a result, burning of the plating tends to occur. 20
If it exceeds 0 g / l, waste of ions due to drag-out cannot be ignored, and crystallization may occur when the liquid temperature is lowered. Other plating conditions are not particularly limited, but have a pH of 0.5 to 3,
The preferred ranges are a bath temperature of 40 to 70 ° C., a liquid flow rate of 1 m / min or more, and a current density of 20 A / dm ² or more. Optimal conditions can be adopted in consideration of the desired plating composition and current efficiency. In the plating bath, conductivity aids such as Na ⁺ , NH ₄ ⁺ and SiO for further improving corrosion resistance are used.
_2, the oxide particles, such as _{TiO 2, Al 2 O 3,} BaCr
Chromate particles such as O ₄ may be added, and there is no essential problem in the production method of the present invention.

Thus, an electrogalvanized steel sheet containing Cr and an iron group metal can be manufactured, but the Cr content in the plating layer is preferably 5 to 30%. Even if less than 5%, an improvement in corrosion resistance is recognized in comparison with zinc plating, but if it is 5% or more, not only zinc plating but also Zn-N
It exhibits higher corrosion resistance than alloy plating of i, Zn-Fe, etc., and does not easily generate red rust even if, for example, a salt spray test is performed for 500 hours or more. The reason is that Cr does not passivate in the presence of Zn and exhibits sacrificial corrosion protection together with Zn, but the corrosion products formed on the plating surface function as a hardly soluble protective film, and It is presumed to suppress the invasion of corrosion factors. 30% Cr content
If it exceeds, the workability is lowered, which is not preferred. In addition, vanillin or a derivative of vanillin, or a cationic polymer or a polyoxyalkylene derivative, which is a Cr deposition accelerator, may be co-deposited in a small amount in the plating layer. A layer is formed, which is advantageous for moldability.

[0016]

EXAMPLE A cold-rolled steel sheet was degreased with alkali and pickled with a 5% aqueous sulfuric acid solution, and then electroplated under the conditions shown in Tables 1 and 2. Among the Cr precipitation accelerators, PA having an average molecular weight of 10,000, PAS having an average molecular weight of 3500 as a cationic polymer, and polyethylene glycol having an average molecular weight of 1500 as a polyoxyalkylene derivative were used. A sulfate bath was used as the plating bath, and the coating weight was 20 g / m2.
^{And 2} . Table 2 shows the evaluations of the plating composition, corrosion resistance, and appearance thus obtained. Corrosion resistance is measured by salt spray test (JIS
(According to Z2371) for 500 hours, and was determined in the following manner.

◎: Red rust generation 1% or less ：: Red rust generation 10
% Or less △: Red rust generation 50% or less ×: Red rust generation 50% or more For the plating appearance, the glossiness of the plating surface (JIS)
Z8741 Gs (60 °), black glass plate standard value 9
3) was measured and determined in the following manner. ：: Gloss 30 or more ：: Gloss 20 or more Δ: Gloss 10 or more ×: Gloss less than 10

In Tables 1 and 2, Comparative Example 1 has a small amount of Cr precipitation and poor corrosion resistance due to a small amount of vanillin in the plating bath. In Comparative Example 2, Cr was deposited by increasing the current density with the same plating bath composition as Comparative Example 1, but a sufficient Cr content was not obtained, so that the corrosion resistance was insufficient and the appearance was poor. . Comparative Example 3 is a Zn-Ni alloy plating, and although the appearance is good, the corrosion resistance is lower than that of the present invention. On the other hand, all of the examples of the present invention have a Cr content of 5%.
% Of plating is obtained, and both corrosion resistance and appearance are good. Examples 5 to 11 of the present invention are examples in which vanillins are used in combination with a cationic polymer or a polyoxyalkylene derivative, and the appearance is further improved as compared with the examples of vanillins used alone in Examples 1 to 4 of the present invention, The result that the content rate also became high was obtained.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

As described above, according to the present invention, by adding a specific additive to a plating bath, it is possible to co-deposit Cr into electrogalvanized plating, which has been difficult in the past, and to achieve extremely excellent corrosion resistance. It is for producing electrogalvanized steel sheets.
Therefore, it is extremely effective in producing a rust-preventive steel sheet requiring high corrosion resistance mainly for an automobile body.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amounts of vanillin and PA added to a plating bath and the Cr content in a plating layer;

FIG. 2 is a diagram showing the relationship between the amount of vanillin and PA added to a plating bath and the appearance of a plating film obtained.

Claims (2)

(57) [Claims] When producing an electrogalvanized steel sheet containing Cr, 0.1 to 10 g / l of Zn ²⁺ ion, Cr ³⁺ ion and vanillin or a derivative thereof are contained.
And, using a plating bath which is PH0.5～3.0, current
A method for producing a zinc-based electroplated steel sheet having excellent corrosion resistance, wherein electroplating is performed at a density of 20 to 150 A / dm ² . 2. When producing an electrogalvanized steel sheet containing Cr, 0.1 to 10 g / l of Zn ²⁺ ion, Cr ³⁺ ion, vanillin or a derivative thereof, and 0 to 10 g of a cationic polymer and / or a polyoxyalkylene derivative. 0.1 to 20 g / l at pH 0.5 to 3.0
Using a certain plating bath, a current density of 20 to 150 A /
A method for producing a zinc-based electroplated steel sheet having excellent corrosion resistance, wherein electroplating is performed at dm ² .